Photocopying method



United States Patent 3,382,068 PHOTOCOPYING METHOD Robert M. Gold,Brooklyn, N.Y., assignor to Itek Corporation, Lexington, Mass, acorporation of Delaware No Drawing. Continuation-impart of abandonedapplication fier. No. 137,476, Sept. 7, 1961. This application June 22,1966, Ser. No. 559,386

11 Claims. (Cl. 96--27) ABSTRACT OF THE DISSLOSURE A method of recordingan image pattern of activating radiation comprising exposing imagewise acopy medium comprising at least one photosensitive semiconductor pigmentwhich becomes activated upon exposure to activating radiation and thefirst of two components of a colorforming oxidation-reduction reactioncomposition, and then applying to at least exposed portions of the copymedium the second component of the oxidation-reduction reactioncomposition, whereby the reaction products of the first and secondcomponents of the oxidation-reduction reaction composition form apermanent, irreversible image.

This application is a continuation-impart of patent application Ser. No.137,476 filed Sept. 7, 1961, now abandoned.

The present invention relates to a process of photoimaging and moreparticularly to a method of photocopying employin semi-conductormaterials.

Various types of photographic and reproduction materials and methods areknown, a number of which employ semi-conductor and photo-conductivematerials. One popular imaging method is the electrophotographic processwhich employs a coating of photoconductive pigments on a carrier sheetmaterial of electroconductive properties. Applying to thephotoconductive layer a uniform electrostatic charge and exposing thelayer to a light image results in an imagewise distribution ofdifferentially charged areas on the sheet material. The chargedistribution is then developed to a visible image by application of asuitable finely divided toner material which adheres selectively to theelectrostatically charged portions of the coated base sheet. Althoughthe electrophotographic method has found wide use, it remainsparticularly expensive in view of the equipment requirements and thepreparation of highly specialized base sheet materials.

A method related to electrophotography is the photocondnctographicprocess which employs the photoconductive activity associated withsemi-conductor pigment materials similar to those used inelectrophotography and by photo-imaging creates an imagewisedistribution of current-conducting pathways through the copy material.Such areas of selective conductivity are employed, with currentapplication and developer compositions including electroplatingmaterials, to produce visible images corresponding to the imagewisedistribution of the conductive pattern. As With the electrophotographicprocess, the base sheet materials are generally required to beconductive and copying equipment is expensive and particularlycomplicated.

According to the present invention, a copying method is provided whichmakes use of the electrophotographic 3,382,068 Patented May 7, 1968properties of semi-conductor pigment materials, but which may beaccomplished inexpensively without the use of complicated equipment andwhich further makes use of less expensive, non-conducting base sheetmaterials.

Photocopying processes have previously been described, for example byLevinos in US. Patent 3,052,541, which employ a combination ofsemi-conductor pigments and solutions of reducible ions. Imagewise lightexposure of the pigment/ ion combination results in the reduction of theion to form an immediately visible image. A particular disadvantage ofsuch photo-imaging methods has been the requirement that thephoto-reactive composition be in a fluid condition or at least under theinfluence of a fluid medium during the moment of photo exposure. Thecapability of such methods to provide constant density images is greatlydependent upon the uniformity of conditions of fluidity or moisturecontent over the whole of the copy sheet surface during photo exposure.Particularly expensive equipment and close operative attention tomaterial manipulation are therefore particularly important, andrepresent significant disadvantages.

It has now been found according to the present invention thatconstant-density images may be prepared through the use ofphotolytically-initiated oxidation-reduction color-forming reaction, butwithout the attendant disadvantages of maintaining moist reaction media,as previously noted. The invention generally provides a photocopyingmethod in which a copy sheet comprising a uniform coating of asemi-conductor pigment on a carrier sheet is sensitized to actinicradiation by the application of one component of an oxidation-reductioncolorforming reaction, for example, readily reducible noble metal ions,such as from a coating of a solution of silver nitrate. The sensitizingcoating is dried, thereby eliminating the uneven reaction densitiesexperienced with earlier photolytic reduction copying methods dependentupon moist sensitized surfaces. The dried, sensitized photocopyingmaterial is then imagewise exposed to actinic radiation and a visibleimage is subsequently developed by application of a second component ofthe oxidationreduction color-forming reaction. Materials useful ascooperative color progenitors with readily reducible metal ionsensitizing compositions include normally colorless oxidizable secondarypolyamine color formers such as derivatives of paraphenylene diamine,dimethyl aniline, and

orthotolidine.

The application of the cooperating color progenitors may be reversedwith the same advantageous effectthat is, the oxidizable polyamine maybe applied and dried prior to exposure, and the reducible metal ionsolution applied after exposure as the image-developing composition.

The semi-conductor pigments useful in the materials of the presentinvention include the zinc oxide, titanium dioxide, lead chromate andlead molybdate normally employed in the aforementionedphotoconductographic, electrophotographic, and photochemical copyingmethods. The variations in response of these semiconductor pigments indifferent actinic radiation spectra bands is well known and thesedifferences in properties may be advantageously employed in the methodof the present invention in the manner similar to their use in theabovementioned prior copying methods. Thus, for example, zinc oxide maybe used as the semiconductor pigment when radiations in the nearultraviolet range are anticipated, or others of the noted pigmentmaterials may be used where response to longer wave lengths of light isdesired. Advantageously, mixtures of the various pigments may be usedand a resulting broader spectrum response is obtained.

Supporting sheet materials may be selected from any of the large numberof available paper and plastic films. Such selection need depend onlyupon the preference of the manufacturer, since no special properties,such as electroconductivity, need be provided. The application of thesemiconductor pigment coatings to selected base materials isaccomplished by means of normal coating techniques and coatingcompositions will preferably include up to about 25% of a relativelyinert insulating binder resin material. Where the natural surface of aselected base sheet material normally resists the application ofcoatings, for example when a plastic film such as polyethyleneterephthalate is used, priming or subbing coatings are advantageouslyapplied.

The amounts of sensitizing and developing compositions applied inaccordance with the present copying process may vary over a substantialrange depending upon the base sheet material, pigment composition,coating conditions, and intended conditions of use such as exposureintensities, temperatures, and the like. It is anticipated that suchprocedural details may be readily determined in the light of operatingconditions selected according to the preference of the particularoperator.

It has been generally found, however, that sensitizing and developingcompositions of less than about 5% of reactive material in a suitablesolvent will be fully effective for most applications when applied by anon-metering method such as dip-coating with removal of excess solutionand subsequent drying.

The present invention will be more apparent with reference to thefollowing examples setting forth some preferred embodiments of thepresent photo-imaging process.

Example 1 A coating composition of about 75 parts of titanium dioxidedispersed in a resinous solution binder containing about 25 parts of astyrene-butadiene polymer is applied in a uniform coating on a paperbase sheet. After drying, the pigment coated sheet is dipped in analcoholic 3% solution of silver nitrate. The excess solution is wipedoff and the sheet dried. The sheet material thus sensitized is exposedto light through a master transparency in an ordinary photoproj'ectiondevice. Subsequent to exposure, a 1% alcohol solution of2,2'-dinaphthyl-para-phenylenediamine is applied to the photo-exposedsurface, and the excess developer solution is wiped from the surfacewhen a sufficiently dense image is obtained. Similar dense images areobtained with polyarnine developer solutions containing about 1%4,4,4"-methylidyne tris (N,N') dimethyl-aniline, or orthotolidine.

Example 2 The semi-conductor pigment coating of Example 1 is dip-coatedwith a 1% alcohol solution of N,N'-dinaphthyl para-phenylene diamine,the excess wiped from the surface, and the coated material dried. Thesurface thus sensitized is light-exposed through a master transparencyby ordinary contact exposure means and is then developed with a solutionof 3% silver nitrate in alcohol to obtain a dense image in thelight-struck areas. The developed copy material is washed and dried toprovide a fixed image. Fixing may also be accomplished by contacting thedeveloped surface with thiourea, preferably in an alcohol solution.While the inclusion of a solvent such as alcohol is preferred as a meansof improving penetration with higher binder content compositions,aqueous vehicles are fully satisfactory when lower binder proportionsare used.

The above examples have been presented for the purpose of illustrationand should not be taken to limit the scope of the present invention. Itwould be apparent that the described examples are capable of manyvariations and modifications which are likewise to be included withinthe scope of the present invention as set forth in the appended claims.

What is claimed is:

1. A method of photo-imaging which comprises:

(a) providing a support having on a surface thereof a uniform coatingcomprising a semi-conductor pigment;

(b) uniformly applying to the surface of said coated support a fluidcomposition comprising the reducing agent component of a color-formingoxidation-reduction reaction composition;

(0) drying the coated surface of said support;

(d) imagewise exposing said coated surface to photoactinic radiation;and

(e) uniformly applying to said exposed surface a fluid compositioncomprising the oxidizing agent component of said oxidation-reductionreaction composition, whereby the reaction products of the reducingagent component and oxidizing agent component form a dense, visibleimage in the light-struck areas.

2. The method according to claim 1 wherein the reducing agent componentis a normally colorless oxidizable secondary polyarnine color-former,and the oxidizing agent component is a readily reducible noble metalion.

3. The method according to claim 1 wherein said support coating consistsessentially of a uniform dispersion, in an insulating resinous bindermaterial, of a semiconductor pigment selected from the group consistingof zinc oxide, titanium dioxide, lead chromate, lead molybdate, andmixtures of said pigments.

4. The method of recording an image pattern of acti vating radiationcomprising exposing imagewise a copy medium comprising at least onesemiconductor pigment which becomes activated upon exposure toactivating radiation and a normally colorless oxidizable secondarypolyarnine selected from the group consisting of N,N'-dinaphthyl-para-phenylene-diamine; 4,4,4methylidynetris-(N,N')dimethyl-aniline; and orthotolidine and thenapplying to at least exposed portions of the copy medium the oxidizingagent component of the oxidation-reduction reaction, whereby thereaction product of the reducing agent component and the oxidizing agentcomponent of the oxidation-reduction form a permanent, irreversibleimage in the exposed areas of the copy medium.

5. The method according to claim 4 wherein the semi conductor pigment isat least one member from the group consisting of zinc oxide, titaniumdioxide, lead chromate, and lead molybdate.

6. A method of recording an image pattern of activating radiationcomprising exposing imagewise a copy medium comprising at least onephotosensitive semiconductor pigment which becomes activated uponexposure to activating radiation and a reducing agent component of acolor-forming oxidation-reduction reaction composition and then applyingto at least exposed portions of the copy medium the oxidizing agentcomponent of the oxidation-reduction reaction composition, whereby thereaction products of the reducing agent component and the oxidizingagent component of the oxidation-reduction composition form a dense,visible image in the exposed areas of the copy medium.

7. The method according to claim 6 wherein the semiconductor pigment isat least one member of the group selected from metal oxides, metalchromates, and metal molybdates.

8. A method according to claim 6 wherein the semiconductor pigment is atleast one member selected from the group consisting of zinc oxide,titanium dioxide, lead chromate and lead molybdate.

5 9. A method as in claim 8 wherein the oxidizing agent component of theoxidation-reduction reaction composition comprises silver ion.

10. The method according to claim 6 wherein the oxidizing agentcomponent is a readily reducible noble metal 5 ion, and the reducingagent component is a normally colorless oxidizable secondary polyamine.

11. The method according to claim 10 wherein the polyamine is selectedfrom the group consisting of N,N'- dinaphthyl-para-phenylene-diamine;4,4,4" methylidynetris-(N,N')dimethylaniline; and orthotolidine.

6 References Cited UNITED STATES PATENTS 3,082,085 3/1963 Miller et a1.96-1 3,152,903 10/1964 Shepard et a1. 96-64 NORMAN G. TORCHIN, PrimaryExaminer. J. TRAVIS BROWN, Examiner. C. E. VAN HORN, Assistant Examiner.

